1. Technical Field
The present invention relates to stators for electric rotating machines that are used in, for example, motor vehicles as electric motors and electric generators.
2. Description of Related Art
There is disclosed, for example in Japanese Unexamined Patent Application Publication No. H11-164504, a stator for an electric rotating machine which includes a stator coil formed by joining corresponding pairs of ends of electric conductor segments. The stator coil has a double annular structure. More specifically, the electric conductor segments forming the stator coil are comprised of a plurality of pairs of large and small U-shaped electric conductor segments. For each electric conductor segment pair, turn portions of the large and small electric conductor segments have substantially the same shape and are twisted in the same direction so as to extend in the same direction. Further, the turn portion of the small electric conductor segment is surrounded by the turn portion of the large electric conductor segment so as to extend on the inner side of the turn portion of the large electric conductor segment.
With the above structure, however, it may be difficult to effectively cool the turn portions of the small electric conductor segments. More specifically, as described previously, the turn portions of the large electric conductor segments have substantially the same shape and the same extending direction as those of the small electric conductor segments. Therefore, when cooling air is supplied from the radially inside to coil ends of the stator coil, which are made up of the turn portions of the large and small electric conductor segments, the cooling air first makes contact with the turn portions of the large electric conductor segments and then changes its course to pass by the turn portions of the large electric conductor segments. Consequently, the turn portions of the large electric conductor segments can be effectively cooled by the cooling air. However, the turn portions of the small electric conductor segments, which are located on the inner side of those of the large electric conductor segments, will be shielded from the cooling air by the turn portions of the large electric conductor segments. As a result, the turn portions of the small electric conductor segments may not be effectively cooled by the cooling air.